This invention relates to improvements in helicopter aircraft, and more particularly to an improved helicopter rotor blade for minimizing danger resulting from fatigue failures in the main rotor blades.
In helicopter aircraft, the main rotor blades provide the primary lift forces for supporting the aircraft in flight. The main rotor blades are attached to rotate with the rotor mast.
Conventionally, each main helicopter rotor blade comprises a nose spar extending the length of the blade with one end coupled to the rotor mast. The nose spar provides the main centrifugal load path for the blade components. A trailing skin is attached to and supported by the nose spar to provide lift surfaces. A tip member is attached to the outboard end of the nose spar to seal the outer end of the blade. A trailing closure channel extends along and is attached to the interior of the nose spar. The remainder of the blade is filled with lightweight material to give the blade rigidity. During rotation of the main rotor vibration and centrifugal stress are created within the blades. In some instances, these stresses will produce a fatigue failure in the nose spar, causing one of the main rotor blades to break and the aircraft to lose its lift and crash without warning to the occupants. Advanced fatigue damage to a blade may be evidenced only by a small crack in the rotor blade which is difficult to detect and avoid failure.
It is therefore a feature of the present invention to provide an improved rotor blade having a centrifugal loading structure allowing the aircraft to fly for a limited period of time should a nose spar fail.
In accordance with the present invention, there is provided an improved rotor blade having a metallic load carrying nose spar supporting a trailing section. A secondary centrifugal load bearing member is provided for assuming the centrifugal blade loads for a short period of time should the nose spar fail during use to allow safe landing of the aircraft.
In accordance with a more specific aspect of the present invention, an improved rotor blade is provided including a nose spar extending the length of the leading edge of the blade and open to the rear at upper and lower trailing edges. A mating channel closure member extends along the length of the nose spar and is attached to the inside of the upper and lower trailing edges thereof. The trailing portion of the blade is formed by a skin filled with lightweight material. Bands of unidirectional fiberglass material are attached to the flanges of the closure member and extend the length thereof. The fiberglass bands have a modulus of elasticity substantially lower than that of the nose spar and provide a redundant centrifugal load path in the event that the nose spar should fail during use of the aircraft.